OFDM is a technique that used multiple sub-carriers to convey information. A typical OFDM symbol includes multiple data sub-carriers and optional pilot sub-carriers. Various networks, including Ultra Wide Band networks utilize OFDM techniques.
FIG. 1 is a schematic illustration of two ultra wide band wireless networks (also referred to as personal access networks) 10 and 20, each including multiple devices that wirelessly communicate with each other. First network 10 includes first till third devices A-C 11-13 and the second network 20 includes forth till sixth devices D-F 24-26. The devices exchange information and utilize channel estimation sequences in order to properly receive transmitted information.
Due to various regulations Ultra Wide Band (UWB) symbols include guard sub-carriers with redundant information. The ratio between the power of guard sub-tones and the power of data tones (also referred to guard to information power ratio) is not fixed. Each vendor can define a certain ratio, as long as the power ratio falls within an allowed power ratio range.
OFDM symbols propagate through a wireless medium that usually changes its characteristics over time and even over frequencies. In order to allow proper reception of OFDM symbols an UWB transmitter transmits to a receiver a predefined channel estimation sequence. The receiver compares the receiver channel estimation sequence to the expected predefined sequence and extracts the channel response. After learning the channel response the receiver can reconstruct various received symbols.
Various OFDM devices and OFDM channel estimation methods are described in the following patents, patent applications and articles, all being incorporated herein by reference: U.S. Pat. No. 6,640,088 of Thomas el at, titled “Method and system for adaptive channel estimation techniques”; European Patent Application EP1416689 titled “Channel estimation using the guard interval of a multicarrier signal”; European Patent Application EP141477, titled “Channel estimation for OFDM using orthogonal training sequences”; PCT application publication number WO 03/100986, titled “System and method for data detection in wireless communication systems”; PCT application publication number WO 03/052979, titled “Method and system for adaptive channel estimation techniques”; PCT application publication number WO 02/23850, titled “OFDM communication methods and apparatus”; U.S. patent application publication No. 2003/0210749 of Asjadi, titled “receiver”; “OFDM channel estimation in the presence of asynchronous interference”, by A. Jeremic, T. A. Thomas, and A. Nehorai, 2003 IEEE International Conference on Acoustics, Speech, and Signal Processing, 2003, and “A study of channel estimation in OFDM systems”, by S. Coleri, M. Ergen, A. Puri and A. Bahai, 2002 IEEE.
One of the problems associated with UWB OFDM networks is a relatively high peak to average ratio of the transmitted symbols. This can require very linear high power transmitters and also require low noise receivers that are characterized by a high dynamic range. Various solutions were suggested to solve this problem. One of the solutions includes duplicating an input data stream with multiple different sequences and selecting the product that is characterized by the lowest peak to average ratio.
There is a need to provide a device and method for OFDM channel estimation that is characterized by a low peak to average ratio over a range of data to guard sub-carrier power ratio.